The prospero-related homeobox transcription factor 1, Prox1, is important for the embryonic development of various organs (1) including the eye, liver, pancreas, lymphatic system, heart and the central nervous system (CNS) (2). It is a regulator of cell division with impact on e.g. neurogenesis and cancer development and progression. In the CNS, the expression is not restricted to the embryonic development and to precursor cells. Prox1 is a well-known marker for granule cells of the dentate gyrus (DG) during embryonic development, adult neurogenesis but also for mature granule cells in the adult brain (3). Weaker expression can also be detected outside the DG of the adult brain. Prox1 was shown to be expressed in oligodendrocyte progenitors, e.g. in the subventricular zone and the corpus callosum (4) and in a subtype of cortical interneurons (5).